Dehydrated and freeze-dried foods offer excellent shelf-life, good nutritional content, and are very lightweight compared to hydrated foods. These qualities have made dehydrated and freeze-dried foods popular for wilderness backpacking and long-range military operations. Reducing pack weight is very important when carrying equipment in a backpack. It is not uncommon for recreational wilderness backpackers to count every ounce that goes into their packs. Similarly, military packs have become extremely heavy, typically weighing 70 to 90 lbs. In an effort to trim pack weight, Army Special Operations and Marine Corps soldiers carry a freeze-dried ration called the Meal Cold Weather/Long Range Patrol (MCW/LRP). The MCW/LRP can reduce pack weight by a crucial 5 lbs for a 10-day patrol when compared to the conventional Meal, Ready-to-Eat (MRE) ration. However, the use of freeze-dried foods in the wilderness requires a source of clean, hot water. Carrying the water along with the freeze-dried meals negates the weight savings and defeats a main purpose of using these meals.
The current method for water disinfection in the field used by the military is the addition of a chemical disinfectant to the water. This disinfectant is typically either iodine or chlorine plus a flocculating agent. The flocculating agent requires doing a coarse filtration through a cotton cloth. Recreational backpackers also often use chemical disinfectants. The self-heating water purifier and food heating and hydrating invention (also referred to as SHWP) described hereinafter uses three methods for disinfection: heat disinfection, membrane filtration, and chemical disinfection.
In addition to chemical disinfectants, backpackers often use membrane filters or purifiers. These personal water filters require hand pumping, which can be time consuming. Hand-pump water filters also add considerable weight (approx. 1 lb).
Heating of water or food in the wilderness presents another challenge. Wilderness backpackers often use camp stoves fueled by liquid fuels like white gas. These commercial stoves are also used by soldiers. In addition, soldiers use stoves that use other fuel sources such as flammable gels (e.g., pyropac) and bars (e.g., trioxane). The stove must be set up on a flat, stable surface that is out-of-doors. There are a number of drawbacks to camp stoves. First, they require the carrying of a stove, fuel, and pot which can contribute significant weight (1 to 2 lbs). Second, camp stoves often cannot be used in heavy rains or strong winds. Third, because of toxic fumes and fire concerns, camp stoves can only be used outside. Fourth, camp stoves cannot be used while on the move, either hiking on foot or in a vehicle. The stove presents an additional drawback for military use in that the flame causes a visible and thermal signature that hampers soldier stealth. The SHWP uses a flameless chemical heater and therefore eliminates the need for an open flame and the associated problems. The SHWP can heat water and food while on-the-go (either on foot or in a vehicle), in enclosed spaces (like a tent), in any weather conditions including wind and rain, and without a thermal or visible signature. Also, a disposable version of the SHWP weighs only 3 oz. and therefore offers significant weight savings over the camp stove and hand-pump water purifier it replaces.
The SHWP is also a very flexible device that allows several different specific hardware embodiments and uses. For example, the SHWP can also be used simply to heat water when purification is not required. Also, the SHWP can be used to purify only when cool potable water is desired for drinking. In addition, the SHWP can be used to heat prepared meals, like the MRE, while also heating and purifying water to prepare a hot beverage to accompany the meal or simply to heat a meal and produce hot water for other uses, such as personal hygiene (e.g., shaving). Both flexible, disposable and rigid, reusable embodiments of the SHWP are anticipated.
Flameless chemical heaters are generally well known in the prior art. One such known device is a flameless ration heater (FRH) that uses the exothermic reaction of a supercorroding magnesium/iron (Mg/Fe) alloy with aqueous sodium chloride. These devices use the chemical reaction to provide heat to warm a food or beverage, and any gaseous byproducts of the reaction are vented to the ambient. Mainstream Engineering Corporation of Rockledge, Fla., has also used a chemical reaction to provide a pressure source in addition to heat.
The Mg/Fe-water reaction is the preferred exothermic and pressure-generating chemical reaction for the present invention. The stoichiometry of the reaction is shown below.

The magnesium reacts with water to produce magnesium hydroxide, Mg(OH)2, and hydrogen gas, H2. The hydrogen bubbles to the surface while the magnesium hydroxide forms a milky white solution with water and eventually starts precipitating out as the reaction progresses and the solubility with water is exceeded. The reaction is exothermic and produces a significant amount of heat. The reaction is catalyzed by the addition of iron (Fe), which is mechanically alloyed with the magnesium, and sodium chloride (NaCl), which dissolves in the water. The Mg/Fe powder is a commercially available product.
This known chemistry and its use to heat food and water is described in various patents. U.S. Pat. No. 4,522,190 describes the original FRH that used the Mg/Fe powder in a porous sintered plastic sheet. U.S. Pat. No. 5,117,809 discusses an improvement to the FRH reaction that uses the Mg/Fe powder directly rather with the polymer matrix. U.S. Pat. No. 5,611,329 discusses the use of the Mg/Fe powder in a flexible, porous pouch, an approach currently used by the U.S. military for heating MREs. U.S. Pat. No. 5,517,981 describes the use of alternative salts to change the quantity of hydrogen gas produced. U.S. Pat. No. 6,248,257 describes other exothermic chemistries that can be used for heating. None of the prior art sought, however, to harness and use the pressure generated by the reaction.
Hand-pumped, personal water purifiers are also generally well known in the prior art. Possible types of microbial contamination in water are viruses (e.g., norovirus, rotovirus), bacteria (e.g., salmonella, e. coli), and cysts (e.g., giardia, crytosporidium). Most membranes remove microbes by filtering based on size. Water molecules are smaller than the microbes so water passes through the membrane while the microbes are retained. Of the microbes, viruses are the smallest and thus the hardest to remove. While viruses are not typically found in bodies of water in the United States, they are found in other developing countries. Membrane filters that can remove viruses are referred to as purifiers, while membranes that are only effective against bacteria and cysts are referred to as filters.
U.S. Pat. Nos. 5,558,762 and 6,010,626 describe hand-pumped water filters that use ceramic or similar filters to remove bacteria and cysts. U.S. Pat. No. 7,438,801 describes a hand-pumped water purifier for reverse osmosis that removes salt and other contaminants.
Several types of membranes are available for water filtration and purification. Nanofilters have very small pore sizes and are capable of removing viruses. Ultrafilters have larger pores and effective against bacteria and cysts but not viruses. Microfilters have still larger pores and are often used as prefilters to catch plant material and other large contaminants before they contact a finer pore-size filter. Reverse osmosis membranes have very small pores capable of removing salt (NaCl) from saline water sources. Typically, as the pore size is decreased, more pressure is required to push water through the membrane at the same flow rate. Electroadsorptive membranes (see, e.g., U.S. Pat. No. 7,390,343) are a new class of materials that filter based on electrostatic attraction and size. These materials are capable of removing viruses and generally have the filtration performance of a nanofilter with the flow rate of a microfilter.
Mainstream Engineering Corporation of Rockledge, Fla., has previously developed a self-heating, self-hydrating device that also uses the chemical reaction to produce both heat and pressure. Pressure is used to force water through a filtration membrane for purification, and a bladder is relied upon to expand and pressurize the water being forced through the filter.
U.S. Pat. No. 7,709,035 describes a device that combines a chemical heater and membrane filter to heat and purify water for reconstituting freeze-dried foods and beverages. The Mg/Fe heater chemicals are mixed directly with the raw water, and this mixture is then filtered by the membrane. However, this configuration introduces practical problems because the heater chemicals and the magnesium hydroxide byproduct will foul the membrane.
Of the many examples of chemical heaters, hand-pumped water filters, and membranes in the prior art; the present invention improves upon them by combining the heating and purification functions and eliminating the need for a manual hand pump.
An object of this invention is to improve the heating and purification of raw, untreated water of questionable microbial content for the purpose of reconstituting freeze-dried or dehydrated meals or beverages. The function of the invention is to produce potable water at approximately 150° F. (65° C.) from any non-saline water source, including those contaminated with viruses, while optionally also heating a sealed ready-to-eat food pouch.
The present application describes improvements to the above-mentioned Mainstream Engineering Corporation device as described in U.S. patent application Ser. No. 11/767,672. Specifically, a simple passageway instead of an expandable bladder is employed to allow the gaseous products of the reaction to pressurize the water to be treated. In one currently preferred embodiment, the passageway is a simple open pouch that allows gaseous reaction products to flow from the heater section to the raw water section. Removing the bladder has substantial manufacturing and cost advantages and also allows thinner more flexible materials to be used between the heater and raw water sections. It also allows materials with improved heat transfer characteristics to be used. Any issues relating to the bursting of the bladder are also eliminated. These improvements are deemed critical to developing a more cost effective, manufacturable, and lighter device.
This invention involves the use of an apparatus and method to heat and hydrate foods by way of an exothermic and pressure generating chemical reaction. The chemical reaction can be activated by water or other means. For water activation, any water source, ranging from salt water to fresh water can be used. Water is added to a chemical formulation, generating both heat from the exothermic reaction as well as pressure caused by the formation of gaseous products of the reaction. The exothermic heat from the reaction transfers to the raw water and the pressure provides the driving force for membrane filtration (e.g., electroadsorptive, reverse osmosis, nanofiltration, ultrafiltration, and microfiltration). Additional chemical disinfectants can also be optionally used to augment disinfection. The heating and hydrating system can be used in a flexible or rigid container. Specifically, this invention teaches an improved arrangement of the inner and outer sections of the device to segregate the heater chemicals from the raw water in order to allow heating and pressure-driven filtration of the raw water without contaminating it with the heater formulation or its byproducts.
Still one further object of the present invention is to provide a practical way to heat and hydrate dehydrated beverages and foods, and powdered drink mixes, from non-potable water, using an exothermic and pressure generating reaction so as to harness and use the reaction-generated pressure.
Another object of the present invention is to achieve a way of heating pre-packaged foods, such as the military MRE, while also providing purified hot water for an accompanying hot beverage, or for other purposes such as personal hygiene, including shaving.
Yet another object of this invention is to use flexible pouches and/or rigid containers for the heating and hydrating device.
Yet another object of this invention is to keep the chemical formulation separated from the raw water to avoid membrane fouling while allowing the transfer of heat and passage of pressurizing gas without the need for an expandable bladder.
Yet another object of this invention is to allow any reaction which generates heat and pressure to be used in an integrated design to heat and purify non-potable water. Reactions which can generate both heat and pressure can be activated by processes including, but not limited to, water addition, spark, shock, squib, or electrical impulse.
Yet another object of this invention is to use reaction-generated pressure to drive a membrane filtration with potable water fluxes of about at least 4 milliliters per square centimeter per minute.
Yet another object of this invention is to employ chemical compositions that can heat water or food supplies to more than 150° F. (65° C.) in 15 minutes or less.
Yet another object of this invention is to make otherwise non-potable water of questionable microbial origin potable through the removal or inactivation of waterborne bacteria, viruses, and cysts.
A further object of this invention is to be able to use additional chemical disinfectants to augment disinfection of the non-potable water, where the chemical disinfectants can be later removed from the raw water by the membrane so as not to affect the taste.
The SHWP offers flexibility to the user, so certain combinations of one or two of these disinfection methods can also be used, as discussed below. Use of multiple disinfection methods provides maximum redundancy that decreases the chances of device failure. An annoyance with chemical disinfectants such as iodine and chlorine is that they impart a disagreeable taste on the water. The membrane used in a currently preferred embodiment of the SHWP removes the chemical disinfectant after it has killed any microbes present in the raw water and hence does not affect the taste.
The SHWP uses a unique arrangement that uses heat from the reaction to assist in the disinfection, and optionally heat the food or beverage while the reaction generated pressure is used to drive the raw water through the membrane for purification and removal of undesirable chemical tastes, rather than employing manual pumping to create this pressure.